![]() ![]() Other important hormones such as jasmonic acid, salicylic acid and ethylene are also reported to induce senescence in plants (He et al., 2002, Jibran et al., 2013, Yoshimoto et al., 2009, Zhang et al., 2018, Morris et al., 2000). ABA has been reported to accelerate leaf senescence as ABA is shown to induce many genes associated with senescence (Quiles et al., 1995). ![]() ![]() Several hormonal signalling pathways has been associated with process of senescence. ANAC046, SlNAP2 and AtORE1 are some of the examples where NAC transcription factor accelerates the chlorophyll degradation during senescence by directly binding and elevating the expression of chlorophyll catabolic pathway genes (Oda-Yamamizo et al., 2016, Qiu et al., 2015, Ma et al., 2018). SenNACs are reported to induce senescence through direct regulation over chlorophyll catabolic pathway genes such as HCAR, NYC1/ NOL, SGR1, PAO and PPH (Masuda and Fujita, 2008). Transgenic plants overexpressing ANAC032 shows accelerated senescence with higher accumulation of H 2O 2 suggesting that ANAC032 induces ROS for senescence induction (Mahmood et al., 2016). Arabidopsis ore1, ore3, and ore9 mutant plants shows delayed leaf senescence and retain better photosynthetic efficiency and chlorophyll content after application of methyl-viologen or H 2O 2 (Woo et al., 2004). Expression of AtORS1 follows a positive correlation with H 2O 2 exposure and AtORS1 expression reduces chlorophyll content and induces genes involved in senescence and H 2O 2 responses (Balazadeh et al., 2011). Oxidative stress induced by senNACs is a common component of senescence onset in plants. AtNAP ( AtNAC029), ORE1 ( ANAC092/ AtNAC2), ORS1(ANAC059), AtNAC016, OsNAP and SlNAP2 are senNACs reported to have association with stress responses and senescence induction in various plants (Guo and Gan, 2006, Kim et al., 2009, Balazadeh et al., 2011, Kim et al., 2013, Liang et al., 2014, Ma et al., 2018). Senescence is a genetically programmed mechanism of cell death and chlorophyll degradation by a battery of genes which in turn are governed by master regulators such as members of NAC ( NAM, ATAF and CUC2) transcription factors family (Liang et al., 2014, Gregersen and Holm, 2007). Senescence inducing major factors are progressive aging, qualitative hormonal modulation and stress inducing factors such as drought, darkness and biotic agents (Jiang et al., 1993, Bohnert et al., 1995). Senescence involves nutrient remobilization from old tissues to developing organs and supports reproductive growth during life cycle of plants (Quirino et al., 2000). Thus, MpSNAC67 is a master regulator of stress mediated senescence in banana plants. MpSNAC67 is induced under salinity stress, drought and exposure of SA, ABA and methyl-jasmonate suggesting that MpSNAC67 coordinate different stress signals to finetune SA-mediated senescence in plants. ORS1-like is strongly induced under natural senescence while MpSNAC67 is not suggesting that MpSNAC67 coordinate stress-specific senescence to age dependent senescence. MpSNAC67 induces SA mediated senescence as evident by elevated chlorophyll-content and suppression of senescence associated genes such as ORS1-like in snac67 plants. ROS accumulation, a function of SA-pathway was significantly diminished in snac67 plants as evident by induction of antioxidant genes in snac67 plants and suppression in SNAC67-Oxp plants. Suppression of NCED-like and ABA3-like in SNAC67-Oxp plants and reduced ABA content in snac67 knockout plants suggest that MpSNAC67 functions through ABA independent pathways. MpSNAC67 induces ICS1 while it suppresses SAGT1 causing reduced SA content in snac67 plants which suggest that MpSNAC67 functions through SA mediated pathways. Here, we report the functions of MpSNAC67, a NAC transcription factor from banana in regulating the stress induced senescence through coordination of senescence associated genes and SA content. Senescence associated NAC transcription factors have been reported to control ABA-mediated senescence however, their regulation over salicylic acid (SA) mediated senescence has not been studied. Stress induced senescence negatively impact yield but is a crucial factor for reproductive growth and thus ensues the evolutionary success of crops. ![]()
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